Acoustical dry product density sensor

Abstract

A device for installation on the auger filler cone of dry product dispensing equipment which comprises one or more ultrasonic resonators arranged so as to measure the acoustic impedance of the product within the auger filler cone without interfering with the flow of the augered product. The acoustic impedance can be calibrated to give a density measurement. The device is particularly well-suited for measuring the density of a dry product in the dispensing equipment used in the packaging industry, where a specified amount by weight must be dispensed into containers. Since an auger-type filling machine dispenses a precise volume for each degree of rotational movement of the auger, constant monitoring of the density of the product within the auger cone allows the weight of the dispensed product to be rapidly and accurately determined during the filling process.

What is claimed is: 
     
       1. In combination with an auger-type product dispensing machine, a device for adjusting the volume of product dispensed as a function of the density of product near the bottom of the filler cone of said dispensing machine in order to dispense an accurate amount of weight of said product comprising: (A) at least one measuring pair of acoustical resonators, one resonator of each pair being a driving resonator, the other being a driven resonator, said pair being positioned near the bottom of said filler cone so that the sensing surface of said driving resonator is in acoustical contact with said product, said driven resonator being mechanically coupled to said driving resonator so that a vibration produced by said driven resonator will induce a signal voltage in said driven resonator, said signal voltage being used in a feedback loop to vary the voltage fed to said driven rsonator in order to maintain the magnitude of vibration produced by said driven resonator essentially constant; and   (B) means for equating changes in the voltage level required to maintain a constant magnitude of ultrasonic vibration output from said driven resonator with changes in the density of said product.   
     
     
       2. The device of claim 1 which further comprises a reference pair of resonators identical to said at least one measuring pair, except that the driving resonator of said reference pair is preloaded with a material of known density, the voltage level induced in said driven reference resonator being compared with the voltage level required to maintain constant the constant magnitude vibration produced by said driven measuring resonator. 
     
     
       3. In combination with an auger-type product dispensing machine, a device for adjusting the volume of product dispensed as a function of the density of product near the bottom of the filler cone of said dispensing machine in order to dispense an accurate amount by weight of said product comprising: a reasuring acoustical resonator positioned near the bottom of said filler cone and having its sensing surface in acoustical contact with said product; and   means for equating changes in the acoustical impedance of said resonator with changes in the density of said product, said equating means comprises: means for applying an oscillating force having a variable frequency sweeping through the antiresonant characteristic frequencies of said resonator;   means for detecting the maximum acoustical impedance of the resonator as the frequency of said oscillating force reaches the antiresonant characteristic frequency of said resonator; and   means responsive to said means for detecting, for controlling the angular rotation of said auger, said responsive means for controlling comprises means for stopping the movement of said auger as a function of its rotational travel multiplied by the detected maximum acoustical impedance.     
     
     
       4. The device of claim 3 wherein said means for stopping comprises: (A) an optical encoder coupled to the auger drive shaft, said optical encoder generating a discrete pulse for each given increment of said auger's angular movement;   (B) a rate multiplier designed to multiply the cumulative value of said discrete pulses by a value proportional to said maximum acoustical impedance; and   (C) a comparator for monitoring the output of the rate multiplier and for generating an auger stopping signal when said output reached a predetermined limit.   
     
     
       5. The device of claim 3 wherein said means for stopping comprises: (A) an optical encoder coupled to the auger drive shaft, said optical encoder generating a discrete pulse for each given increment of said auger's angular movement;   (B) a rate multiplier designed to multiply the cumulative value of said discrete pulses by a value proportional to said maximum acoustical impedance; and   (C) a comparator for monitoring the output of the rate multiplier and or generating an auger stopping signal when said output reaches a predetermined limit.   
     
     
       6. In combination with an auger-type product dispensing machine, a device for adjusting the volume of product dispensed as a function of the density of product near the bottom of the filler cone of said dispensing machine in order to dispense an accurate amount by weight of said product comprising: a measuring acoustical resonator positioned near the bottom of said filler cone and having its sensing surface in acoustical contact with said product; and   means for equating changes in the acoustical impedance of said resonator with changes in the density of said product, said equating means comprises: means for applying an oscillating force having a variable frequency sweeping through the antiresonant charactertistic frequencies of said resonator;   means for detecting the maximum acoustical impedance of the resonator as the frequency of said oscillating force reaches the antiresonant characteristic frequency of said resonator, said means for detecting comprises an analog-to-digital converter;   means for advancing said analog-to-digital converter one bit for each cycle of said oscillating force;   a ladder network for converting the output of said analog-to-digital converter into a tracking voltage; and   an analog signal comparator, said comparator receiving said tracking voltage at its reference terminal and a signal proportional to said acoustical impedance at its input terminal; and   said comparator further controlling the input of said analog-to-digital converter; and means, responsive to said means for detecting, for controlling the angular rotation of said auger.         
     
     
       7. In combination with an auger-type product dispensing machine, a device for adjusting the volume of product dispensed as a function of the density of product near the bottom of the filler cone of said dispensing machine in order to dispense an accurate amount by weight of said product comprising: (A) a measuring acoustical resonator positioned near the bottom of said filler cone and having its sensing surface in acoustical contact with said product; and   (B) means for equating changes in the acoustical impedance of said resonator with changes in the density of said product, said equating means comprises: a. means for applying an oscillating force having a variable frequency sweeping through the resonant characteristic frequencies of said resonator;   b. means for detecting the minimum acoustical impedance of the resonator as the frequency of said oscillating force reaches the resonant characteristic frequency of said resonator; and   c. means responsive to said means for detecting, for controlling the angular rotation of said auger, said means for controlling comprises means for stopping the movement of said auger as a function of its rotations rotational travel multiplied by the detected maximum acoustical impedance.     
     
     
       8. In combination with an auger-type product dispensing machine, a device for adjusting the volume of product dispensed as a function of the density of product near the bottom of the filler cone of said dispensing machine in order to dispense an accurate amount by weight of said product comprising: a measuring acoustical resonator positioned near the bottom of said filler cone and having its sensing surface in acoustical contact with said product; and   means for equating changes in the acoustical impedance of said resonator with changes in the density of said product, said equating means comprises: a. means for applying an oscillating force having a variable frequency sweeping through the antiresonant characteristic frequencies of said resonator;   b. means for detecting the minimum acoustical impedance of the resonator as the frequency of said oscillating force reaches the resonant characteristic frequency of said resonator, said detecting means comprises: an analog-to-digital converter;   means for advancing said analog-to-digital converter one bit for each cycle of said oscillating force;   ladder network for converting the output of said analog-to-digital converter into a tracking voltage; and   an analog signal comparator; said comparator receiving said tracking voltage at its reference terminal and a signal proportional to said acoustical impedance at its input terminal; and said comparator further controlling the input to said analog-to-digital converter; and means, responsive to said means for detecting, for controlling the angular rotation of said auger.